fs: Allow superblock owner to access do_remount_sb()

Superblock level remounts are currently restricted to global CAP_SYS_ADMIN, as is the path for changing the root mount to read only on umount. Loosen both of these permission checks to also allow CAP_SYS_ADMIN in any namespace which is privileged towards the userns which originally mounted the filesystem. Signed-off-by: Seth Forshee <[email protected]> Acked-by: "Eric W. Biederman" <[email protected]> Acked-by: Serge Hallyn <[email protected]> Acked-by: Christian Brauner <[email protected]> Signed-off-by: Eric W. Biederman <[email protected]>
olifre · May 24, 2018 · bc6155d · bc6155d
1 parent 0031181
commit bc6155d
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/fs/namespace.c b/fs/namespace.c
@@ -1590,7 +1590,7 @@ static int do_umount(struct mount *mnt, int flags)
 		 * Special case for "unmounting" root ...
 		 * we just try to remount it readonly.
 		 */
-		if (!capable(CAP_SYS_ADMIN))
+		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
 			return -EPERM;
 		down_write(&sb->s_umount);
 		if (!sb_rdonly(sb))
@@ -2333,7 +2333,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 	down_write(&sb->s_umount);
 	if (ms_flags & MS_BIND)
 		err = change_mount_flags(path->mnt, ms_flags);
-	else if (!capable(CAP_SYS_ADMIN))
+	else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
 		err = -EPERM;
 	else
 		err = do_remount_sb(sb, sb_flags, data, 0);